Gravitational redshifts, and other wavelength shifts in stellar spectra

Transcription

1 ESO Santiago, February 2012 KVA Gravitational redshifts, and other wavelength shifts in stellar spectra Dainis Dravins Lund Observatory

2 Exactly 100 years ago

3 Predicted effects by gravity on light A.Einstein, Annalen der Physik 340, 848 (1911)

4 Historical perspectives Predicting gravitational redshift Unsuccessful searches Experimental confirmations Effects in normal stars? Other wavelength shifts Shifts across stellar disks

5 Already long before Einstein

6 Predicting gravitational effects on light John Mitchell (1784)

7 Predicting gravitational effects on light Pierre-Simon Laplace (1796)

8 Verifying Einstein?

9 Freundlich s attempts to verify relativity theory (I) Erwin Finlay Freundlich ( ) worked to experimentally verify the predictions from Einstein s theory of relativity and the effects of gravity on light. Klaus Hentschel: Erwin Finlay Freundlich and Testing Einstein s Theory of Relativity, Archive for History of Exact Sciences 47, 243 (1994)

10 Freundlich s attempts to verify relativity theory (II) Einsteinturm, Potsdam-Telegrafenberg Klaus Hentschel: Erwin Finlay Freundlich and Testing Einstein s Theory of Relativity, Archive for History of Exact Sciences 47, 243 (1994)

11 Unethical falsifications in astronomy? Nature 306, 727 (1983)

12 Controversial interpretations of history QJRAS 26, 279 (1985)

13 Actual gravitational redshift in white dwarfs

14 Stellar spectroscopy

15 Expected gravitational redshifts D. Dravins IAU Symp. 210

16 Mechanisms causing wavelength shifts The process includes: motion of the object; its emission of an electromagnetic signal; its propagation through space; motion of the observer; and the reception of the signal. L.Lindegren & D.Dravins: The fundamental definition of radial velocity, A&A 401, 1185

17 Radial velocities without spectroscopy

18 Astrometric radial velocities I Dravins, Lindegren & Madsen, A&A 348, 1040

19 Astrometric radial velocities II Dravins, Lindegren & Madsen, A&A 348, 1040

20 Astrometric radial velocities from perspective acceleration Dravins, Lindegren & Madsen, A&A 348, 1040

21 Astrometric radial velocities III Dravins, Lindegren & Madsen, A&A 348, 1040

22 Pleiades from Hipparcos Proper motions over 120,000 years

23 Hyades lineshifts Madsen, Dravins & Lindegren, A&A 381, 446

24 Differential velocities within open clusters

25 M 67 Dean Jacobsen, astrophoto.net

26 Searching for gravitational redshifts in M67 Dean Jacobsen, astrophoto.net M67 (NGC 2682) open cluster in Cancer contains some 500 stars; age about 2.6 Gy, distance 850 pc. M67 color magnitude diagram with welldeveloped giant branch. Filled squares denote single stars. L.Pasquini, C.Melo, C.Chavero, D.Dravins, H.-G.Ludwig, P.Bonifacio, R.De La Reza: Gravitational redshifts in main-sequence and giant stars, A&A 526, A127 (2011)

27 Searching for gravitational redshifts in M67 Radial velocities in M67 with a superposed Gaussian centered on Vr = 33.73, σ = 0.83 km s 1 Radial velocities in M67: No difference seen between giants (red) and dwarfs (dashed) L.Pasquini, C.Melo, C.Chavero, D.Dravins, H.-G.Ludwig, P.Bonifacio, R.De La Reza: Gravitational redshifts in main-sequence and giant stars, A&A 526, A127 (2011)

28 Real line formation

29 AN IDEAL STAR? Solar disk June 12, 2009 GONG/Teide

30 Solar Optical Telescope on board HINODE (Solar-B) G-band (430nm) & Ca II H (397nm) movies

31 Spectral scan across the solar surface. Left: H-alpha line Right: Slit-jaw image Big Bear Solar Observatory

32 Wiggly spectral lines of stellar granulation (modeled) Disk-center Fe I profiles from 3-D hydrodynamic model of the metal-poor star HD in NLTE and LTE. Top: Synthetic wiggly-line spectra across stellar surface. Curves show equivalent widths W along the slit. Bottom: Spatially resolved profiles; average is red-dotted. N.G.Shchukina, J.Trujillo Bueno, M.Asplund, Astrophys.J. 618, 939 (2005)

33 Cool-star granulation causes convective lineshifts on order 300 m/s

34 STELLAR CONVECTION White dwarf vs. Red giant Snapshots of emergent intensity during granular evolution on a 12,000 K white dwarf (left) and a 3,800 K red giant. Horizontal areas differ by dozen orders of magnitude: 7x7 km 2 for the white dwarf, and 23x23 R Sun 2 for the giant. (H.-G. Ludwig)

35 F5 G2 IV G2 V K1 Bisectors of the same spectral line in different stars Adapted from Dravins & Nordlund, A&A 228, 203 From left: Procyon (F5 IV-V), Beta Hyi (G2 IV), Alpha Cen A (G2 V), Alpha Cen B (K1 V). In stars with corrugated surfaces, convective blueshifts increase towards the stellar limb Velocity [m/s]

36 Searching for gravitational redshifts in M67 Gravitational redshift predictions vs. mass/radius ratio (M/R) (dashed red) do not agree with observations. Calculated convective wavelength shifts for Fe I lines in dwarf (red crosses) and giant models (squares). L.Pasquini, C.Melo, C.Chavero, D.Dravins, H.-G.Ludwig, P.Bonifacio, R.De La Reza: Gravitational redshifts in main-sequence and giant stars, A&A 526, A127 (2011)

37 Variable gravitational redshift in variable stars? H.M.Cegla, C.A.Watson, T.R.Marsh, S.Shelyag, V.Moulds, S.Littlefair, M.Mathioudakis, D.Pollacco, X.Bonfils Stellar jitter from variable gravitational redshift: Implications for radial velocity confirmation of habitable exoplanets, MNRAS Lett. (2012) Stellar radius changes required to induce a δv grav equivalent to an Earth-twin RV signal. Circles represent (right to left) spectral types: F0, F5, G0, G2, G5, K0, K5 and M0. Dashed curves represent stellar radius variations of 50, 100 and 300 km

38 Spatially resolved spectroscopy across stellar surfaces

39 Exoplanet transit Selecting a small portion of the stellar disk

40 Doppler imaging of stellar surfaces For a star with a dark spot close to the equator, spectral line profiles are affected throughout their whole Width, as the spot is carried around the star by rotation. (Jean-François Donati)

41 Spatially resolved stellar spectroscopy Left: Integrated line profiles V rot = 2, 40, 120 km/s Right: Line behind planet Top: Noise-free Bottom: S/N = 300, R=300,000 (Hiva Pazira, Lund Observatory)

42 Spatially resolved stellar spectroscopy Synthetic line profiles across stellar disks Examples of synthetic line profiles from hydrodynamic 3-D stellar atmospheres. Curves are profiles for different positions on the stellar disk, at some instant in time. Black curves are at disk-center; lower intensities of other curves reflect the limb darkening. Top: Solar model; Fe I, 620 nm, 1 ev. Bottom: Giant model; Fe I, 620 nm, 3 ev. Disk locations cos = µ = 1, 0.87, 0.59, Simulation by Hans-Günter Ludwig (Landessternwarte Heidelberg)

43 Visual high-resolution spectrometers at 8-10 m telescopes Telescope SALT Keck I VLT Kueyen HET Subaru LBT Diameter [m] Spectrometer HRS HIRES UVES HRS HDS PEPSI Maximum R 65,000 84, , , , ,000 Wavelengths [µm]

44 Potsdam Echelle Polarimetric and Spectroscopic Large Binocular Telescope

45 Spatially resolved spectroscopy with ELTs Left: Hydrodynamic simulation of the supergiant Betelgeuse (B.Freytag) Right: Betelgeuse imaged with ESO s 8.2 m VLT (Kervella et al., A&A, 504, 115) Top right: 40-m E-ELT diffraction limits at 550 nm & 1.04 μm.. Hiva Pazira (Lund Observatory)

46 Resolving power and spectral range of proposed E-ELT spectrographs

47 Grand challenge: Design an efficient R = 1,000,000 high-fidelity spectrometer for E-ELT!

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